I. Field of the Invention
The present invention relates to a communication apparatus which can be connected to another communication apparatus.
A key telephone system (to be referred to as a KTS hereinafter) is known as a small PBX system. This KTS comprises a main unit often connected to a network through a plurality of lines, and a plurality of exclusive telephone sets (key telephone sets) connected to the main unit through message and control lines. Each exclusive telephone set includes a connection control key, a hold key, and the like. When message communication is required, the connection control key arranged on each exclusive telephone is depressed to connect this telephone set to the line.
Another conventional apparatus for performing data communication through analog modulation/demodulation, such as a facsimile machine, is known as an apparatus utilizing a telephone line in addition to a speech terminal such as a telephone set. When this data communication apparatus is connected to the KTS, a system may be proposed wherein the apparatus is connected as one of the exclusive telephone sets.
In this system, when the data communication apparatus is set in an automatic incoming call reception mode, the data communication apparatus automatically starts data communication upon detection of a ringing signal. Another system may be proposed wherein the right of reception of an incoming call is assigned to the data communication apparatus upon an operation at a console unit of a main unit or exclusive telephone set to perform automatic incoming call reception, or a priority of reception of the incoming call is assigned to the telephone set, and reception of the incoming call is changed over. Even if the right of reception of the incoming call is controlled as described above, all incoming calls are undesirably received by the data communication apparatus in the automatic incoming call reception mode.
Japanese Patent Publication No. 62-16595 describes an arrangement in which a KTS exclusive telephone set is connected to a data communication apparatus such as a facsimile machine, and the telephone set is used as an adapter of the data communication apparatus. The arrangement of this system is shown in FIG. 1.
In the system described in Japanese Patent Publication No. 62-16595, when a telephone set 32 receives data representing a request for connecting an exchanger 31 to a facsimile machine 33, the telephone set 32 transmits a start signal to the facsimile machine 33. In this case, a message cannot be sent from the telephone set.
A data communication apparatus performs different operations in accordance with whether the data communication apparatus is connected to the line. For example, when a facsimile machine is connected to a line, facsimile communication is performed. However, when the facsimile machine is not connected to the line, the facsimile machine copies an original. For example, in an arrangement shown in FIG. 2, an accessory telephone set 49 and a line 41 are connected to each other through a facsimile machine 42. A control unit 43 in the facsimile machine 42 can cause a switch 45 to detect whether the accessory telephone set 49 is connected to the line 41.
To the contrary, in the system shown in FIG. 1, the exclusive telephone set 32 is connected to the exchanger 31 without being through the facsimile machine 33. Therefore, the facsimile machine 33 cannot detect a connecting state between the telephone set 32 and the exchanger 31.